Further work on negative chemical ionization mass spectrometry has shown its general applicability for very high sensitivity analysis of compounds in biological fluids. Following development of a melatonin assay, similar methods have been applied to the analysis of other indolealkylamines (serotonin, 6-hydroxymelatonin) and a variety of biogenic amines and their metabolites (metanephrine, normetanephrine, 3,4 dihydroxyphenylglycol (DHPG), and 3-methoxy-4-hydroxyphenylglycol (MHPG)). Hexafluoroacetone has been shown to produce stable, highly sensitive derivatives for 1,2 disubstituted compounds. A second mass spectrometer has been converted for negative ion detection. The selected ion recording system developed for use with the LKB 9000 has also been modified to operate with quadrupole mass spectrometers.